Methods and apparatus for supplying flushing fluid to a grinding head

ABSTRACT

Button inserts of a rock drilling bit are ground by positioning a grinding cup against each button insert and rotating the cup while supplying flushing fluid thereto. The flushing fluid is conducted through an axial bore of a spindle on which the grinding cup is mounted. An inner end of the spindle is mounted for rotation in a grinding head, and is rotated by a drive mechanism disposed within the grinding head. Flushing fluid is supplied to the axial bore through a flushing head mounted on the spindle at a location outside of the grinding head. The flushing head has axially spaced parts that are movable axially relative to one another under the force of flushing fluid passing therethrough, in order to establish a fluid seal.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for grindingbuttons of a rock drilling bit, and to a flushing head for supplyingflushing medium.

From Swedish Patent 460 584 a device for grinding buttons of a rockdrilling bit is previously known, said device including a grinding headhaving a rotatably journalled spindle that receives a grinding cup.Inside the grinding head, means are provided for supplyingflushing/cooling medium to a recess of the grinding cup. Saidflushing/cooling medium is supplied axially within the rotatable spindleand then axially within the shank of the grinding cup until theflushing/cooling medium reaches the recess of the grinding cup. However,due to the fact that the means for supplying flushing/cooling medium tothe grinding cup is located within the grinding head, considerablesealing arrangements for separating the flushing/cooling medium from thelubricating medium must be present. This complicates the design of thegrinding head.

The aim of the present invention is to present a method and apparatusfor grinding buttons of rock drilling bits, while simplifying the supplyof flushing/cooling medium to the grinding cup.

SUMMARY OF THE INVENTION

One aspect of the present invention involves a method of grinding abutton of a rock drilling bit, comprising the steps of positioning agrinding surface of a grinding cup against the button; applying a rotaryforce to an inner end of a shaft structure disposed within a grindinghead, to rotate the grinding cup which is mounted on an outer portion ofthe shaft structure disposed outside of the grinding head; introducing aflushing medium to an inlet of an axial bore of the outer portion at alocation disposed outside of the grinding head; and conducting theflushing fluid through the axial bore to the grinding surface forflushing the grinding surface.

An apparatus aspect of the invention comprises a grinding head, a shaftstructure including inner and outer portions, the inner portionrotatably mounted in the grinding head, and the outer portion projectingout of the grinding head. A drive mechanism is connected to the innerportion for rotating the shaft structure. A grinding cup is mounted onthe outer portion and includes a grinding surface for grinding a buttonupon rotation of the shaft structure. The outer portion of the shaftstructure includes an axial bore communicating with the grindingsurface. The axial bore includes an inlet situated outside of thegrinding head. The inlet is adapted to communicate the axial bore with asource of flushing fluid so that flushing fluid can be conducted to thegrinding surface through the axial bore for flushing the grindingsurface.

Another aspect of the invention relates to a flushing head adapted to bemounted on a rotatable grinding spindle which carries a grinding cup,for conducting flushing medium to an axial bore of the grinding spindle.The flushing head comprises a radially inner part having an axialthrough-bore adapted to be mounted on the grinding spindle to be rotatedtherewith. The axially inner part includes a pair of axially spacedsleeves each carrying a seal for creating a fluid seal with the grindingspindle. The sleeves are axially separated by a cylindrical spacer whichincludes a first opening extending radially therethrough at a locationaxially between the seals. The flushing head further includes astationary radially outer part connected nonfixedly to the sleeves insurrounding relationship to the spacer. The radially outer part includesa second opening communicating with the first opening for conductingflushing fluid thereto.

The flushing head preferably permits the sleeves to be moved axiallyaway from one another by a force of the flushing fluid and into sealingrelationship with respective portions of the radially outer portion.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the device/flushing head according to the invention isbelow; reference being made to the accompanying drawings where

FIG. 1 shows a section of a grinding head of the device according to thepresent invention; and

FIG. 2 shows in detail a section of a flushing head of the device shownin FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

As is apparent from FIG. 1 the device according to the present inventionincludes a grinding head 10 that is secured to a power source 12,preferably an electric motor that is only schematically disclosed. Thegrinding head 10 can be displaced vertically, i.e. downwards andupwards, by an arrangement that is not disclosed.

The grinding head 10 includes an outer casing 14 that is stationary. Formounting and service reasons the casing includes an upper section 14Uand a lower section 14L that are coupled to each other by bolts 16.

A protruding shaft 18 of the power source 12 extends into the grindinghead 10, said shaft 18 being rotatable relative to a first longitudinalcenter axis 19. On an intermediate portion of the shaft 18 a gear means20 is mounted, preferably an eccentric gear means. Said gear means 20 iscoupled to a driving sleeve 22 that is located inside the outer casing14. Due to the transmission ratio of the gear means 20 the drivingsleeve 22 is rotated much more slowly than the shaft 18. As typicalvalues can be mentioned that if the shaft 18 rotates at respectively3000 r.p.m. then the driving sleeve 22 rotates about 40 r.p.m.

On the free end of the protruding shaft 18 one end of a cardan joint 24is mounted. The other end of the cardan joint 24 is mounted on anintermediate shaft 26 that is provided with a diameter reduction 28close to the cardan joint 24. Said diameter reduction 28 serves thepurpose to impart a certain flexibility to the intermediate shaft 26 tocompensate in case that the rotation center 30 of the cardan joint 24does not exactly coincide with the longitudinal center axis 19.

The intermediate shaft 26 has a second longitudinal centre axis 27 thatdue to the cardan joint 24 is allowed to form an acute angle α with thefirst longitudinal centre axis 19. The angle α is in the interval5°-15°, with preference for values in the magnitude of 10°.

Integrally with the driving sleeve 22 a spindle house 32 is provided,said spindle house 32 being journalled by first 34 and second 36 ballbearings that are axially spaced apart within the outer casing 14.

The end of the intermediate shaft 26, remote from the cardan joint 24,is journalled in a first boring 38 of the spindle house 32. Said end ofthe intermediate shaft 26 is supported by third 40 and fourth 42 ballbearings that are axially spaced apart, by a first distance sleeve 44,in the longitudinal direction of the intermediate shaft 26. The fourthball bearing 42 is supported by a first step 46 formed in the spindlehouse 32. The longitudinal centre axis of the first boring 38 coincideswith the second longitudinal centre axis 27.

Between the diameter reduction 28 and the third ball bearing 40 a firstgear wheel 48 is mounted, said first gear wheel 48 being axially fixedbetween a collar 50 on the intermediate shaft 26 and a spacing member 52located between the third ball bearing 40 and the first gear wheel 48.In a second boring 54 of the spindle house 32, and inner portion of ashaft structure defined by a grinding spindle 56 is rotatably journalledby fifth 58 and sixth 60 ball bearings that are axially spaced apart, bya second distance sleeve 62, in the longitudinal direction of thegrinding spindle 56. The sixth ball bearing 60 rests on a second step 61formed in the spindle house 32. Since the sixth ball bearing 60 is ofthe double row type, it supports the grinding spindle 56 in both axialand radial directions. The support in the axial direction is effectedvia a collar 64 of the grinding spindle 56. The fifth ball bearing 58 isaxially locked by a washer 66. The rotation of the grinding spindle 56is relative to a third longitudinal centre axis 57 of the grindingspindle 56, said third longitudinal centre axis 57 being parallel to thesecond longitudinal centre axis 27. Thus, the third longitudinal centreaxis 57 also forms the angle α with the first longitudinal centre axis19. The longitudinal centre axis of the second boring 54 coincides withthe third longitudinal centre axis 57.

At its upper end the grinding spindle 56 carries a second gear wheel 68having a considerably smaller diameter than the first gear wheel 48.This means that the grinding spindle 56 will rotate considerably fasterthan the intermediate shaft 26. The protruding shaft 18 rotates with thesame r.p.m. as the intermediate shaft 26. As pointed out above a typicalvalue is 3000 r.p.m. The transmission ratio between the first 48 andsecond 68 gear wheels is typically of such magnitude that the grindingspindle 56 will rotate by about 13000 r.p.m.

Due to the cardan joint 24 it is possible to use gear wheels 48, 68 ofstandard type, i.e. gear wheels having a generally cylindrical outerperiphery.

Between the lower end of the outer casing 14 and the lower end of thespindle house 32 a first sealing means 67 is provided and between thelower end of the second boring 54 and the grinding spindle 56 a secondsealing means 69 is provided. For lubrication purposes oil is present inthe interior of the grinding head 10. The upper level of the oilpreferably reaches the upper part of the spindle house 32. The sealingmeans 67 and 69 have the purpose to prevent oil from leaking out fromthe grinding head 10.

The outer portion of the grinding spindle 56 that protrudes out of thethe outer casing 14 has a free end which carries a flushing head 70 thatis described more in detail in FIG. 2. The flushing head 70 is providedwith two diametrically located openings 71 that receive hoses 72 thatsupply flushing medium from a suitable source (not shown). Theconnection of the hoses 72 to the source prevents a part of the flushinghead 70 to from rotating when the grinding spindle 56 is rotated. Thisis explained more in detail below.

In FIG. 2 the flushing head 70 is shown in a larger scale. The flushinghead 70 includes a radially inner part having two sealing sleeves 74that surround the grinding spindle 56. The sealing against the grindingspindle 56 is effected via an O-ring 76 an axial through-bore in eachsealing sleeve 74, said O-ring 76 being received in an internalcircumferential groove in each sealing sleeve 74. In order to positionthe sealing sleeves 74 axially apart on the grinding spindle 56 there isprovided a spacing tube 77 that surrounds the opposing ends of thesealing sleeves 74 and an intermediate portion of the grinding spindle56. The spacing tube 77 is provided with a number of openings 78 thatadmit flushing medium to the intermediate portion of the grindingspindle 56. The fit between the grinding spindle 56, the O-rings 76 andthe sealing sleeves 74 is such that the sealing sleeves 74, togetherwith the spacing tube 77, are driven when the grinding spindle 56 isrotated. The flushing head 70 further includes a radially outer portionhaving two rings 73 and a house 75. The rings 73 are provided withexternal threads and the rings 73 are mounted in the axial ends of thehouse 75 via cooperating threads in said house 75. The rings 73 and thehouse 75 of the flushing head 70 remain stationary when the grindingspindle 56 is rotated. Thus, there should be friction between thesealing sleeves 74 and the grinding spindle 56 but preferably nofriction between the sealing sleeves 74 and the rings 73.

When the flushing medium within the flushing head 70 is pressurized thesealing sleeves 74 are urged axially apart and there are establishedaxial sealing faces 79 between the rotating sealing sleeves 74 and thestationary rings 73.

As is shown most clearly in FIG. 2, the outer portion of the grindingspindle 56 is provided with a first axial boring 80 that receives ashank 84 of a grinding cup 82, said shank 84 being secured axially by anO-ring 85 mounted in the first axial boring 80. The shank 84 is furtherprovided with a through-going second axial boring 86 that communicateswith a grinding surface that forms a recess 88 in the head of thegrinding cup 82. A key/slot arrangement (not shown) between the head ofthe grinding cup 82 and the free end of the grinding spindle 56 drivesthe grinding cup 82 when the grinding spindle 56 is rotated. A number ofradial borings 90 extend from the periphery of the outer portion of thegrinding spindle 56 to the region of the bottom of the first axialboring 80 thus defining an inlet for establishing a communication forthe flushing medium between the outside of the grinding spindle 56 andthe first axial boring 80.

The device described above according to the present invention functionsin the following way. The grinding head 10 is lowered and simultaneouslythe drill bit is displaced laterally until the recess 88 in the grindingcup 82 is properly positioned relative to the button to be ground. Thedrill bit is then locked in its position. The electric motor 12 isstarted and the driving sleeve 22 and the spindle house 32 rotates, asone unit. When the spindle house 32 rotates it is realized that due tothe fact that the third longitudinal centre axis 57 forms an acute anglewith the first longitudinal centre axis 19 the grinding spindle 56 willmove along a conical envelope surface. The rotation of the spindle house32 is relatively slow, i.e a typical value is about 40 r.p.m. However,simultaneously as the grinding spindle 56 moves along the conicalsurface the grinding spindle 56 itself rotates relative to itslongitudinal centre axis 57. Said last-mentioned rotation isconsiderably faster than the rotation of the spindle house 32, i.e. atypical value for the grinding spindle 56 is 13000 r.p.m. This verylarge difference between the rotation speed of the spindle house 32 andthe grinding spindle 56 is very favourable to the grinding action of thepresent device, i.e. vibrations in the device are reduced to anessential extent.

When the electric motor 12 starts, the supply of flushing medium,preferably water, to the flushing head 70 starts simultaneously. Theflushing medium is supplied to the flushing head 70 via hoses 72 thatare mounted in openings 71 of the flushing head 70. When the flushingmedium has entered the flushing head 70 it passes through the openings78 in the spacing tube 77 and then further through the radial borings 90to the first axial boring 80. The flushing medium then enters the secondaxial boring 86 and emanates in the recess 88 of the grinding cup 82 toprovide flushing/cooling of the button being ground.

The rotating grinding spindle 56 is via the grinding cup 82 performingthe grinding of the chosen button. Since the flushing head 70 ispositioned on the portion of the grinding spindle 56 that is locatedoutside of the grinding head 10 the flushing medium will never enter thegrinding head 10. This is a major advantage as regards a simplifieddesign of the grinding head 10.

The invention is not in any way restricted to the embodiment describedabove but can be varied within the scope of the appending claims.

I claim:
 1. A method of grinding a button of a rock drilling bit,comprising the steps of:A) positioning a grinding surface of a grindingcup against said button; B) applying a rotary force to an inner end of ashaft structure disposed within a grinding head, to rotate said grindingcup which is mounted on an outer portion of said shaft structuredisposed outside of said grinding head; and C) introducing, during stepB, a flushing medium to an inlet of an axial bore of said outer portionat a location disposed outside of said grinding head; and D) conductingsaid flushing fluid through said axial bore to said grinding surface forflushing said grinding surface.
 2. The method according to claim 1,wherein step C comprises conducting said flushing through a lateral boreformed in said outer portion, said lateral bore defining said inlet. 3.The method according to claim 1 including the step of lubricating saidinner portion with a lubricating medium disposed within said grindinghead.
 4. Apparatus for grinding a button of a rock drilling bit,comprising:a grinding head; a shaft structure including inner and outerportions, said inner portion rotatably mounted in said grinding head,and said outer portion projecting out of said grinding head; a drivemechanism connected to said inner portion for rotating said shaftstructure; and a grinding cup mounted on said outer portion andincluding a grinding surface for grinding a button upon rotation of saidshaft structure; said outer portion including an axial borecommunicating with said grinding surface, said axial bore including aninlet situated outside of said grinding head, said inlet adapted tocommunicate said axial bore with a source of flushing fluid so thatflushing fluid can be conducted to said grinding surface through saidaxial bore for flushing said grinding surface.
 5. The apparatusaccording to claim 4, wherein said inlet comprises a lateral bore formedin said outer portion.
 6. The apparatus according to claim 4, whereinsaid shaft structure includes a grinding spindle defining both saidinner and outer portions; a flushing head mounted on said outer portion;said flushing head including a radially inner part connected forrotation with said grinding spindle, and a stationary radially outerpart; said radially inner and outer parts together forming a passagecommunicating with said inlet; said radially outer part having anopening communicating with said passage and adapted for communicationwith the source of flushing medium.
 7. The apparatus according to claim6, wherein said grinding cup includes a hollow shank mounted in saidaxial bore.
 8. The apparatus according to claim 6, wherein said radiallyinner part of said flushing head is removably mounted on said grindingspindle.
 9. The apparatus according to claim 6 further including a hosefor connecting said opening with said source of flushing fluid.